Commercial operations in the production and treatment of iron and steel are known to result in substantial quantities of waste materials which contain iron oxide. These include fines from screened ores, mill scale, blast furnace flue dust, thickener mud and dust from steel mill dust collectors.
Blast furnace charge materials may be screened immediately before charging to eliminate fine particles from the charge. These fines which come from the screening operation contain iron oxides just as do the larger particles used in the furnace charge, but they are too fine to be effectively used as furnace charge materials. Blast furnace flue dust contains fine particles of coke, iron oxides, calcium carbonate and any volatile hydrocarbons that may condense in the gas cleaning system of the furnace. Mill scale is formed during the rolling or working of steel and contains iron oxides along with volatile materials such as grease and oil. Dust from dust collectors on steel melting furnaces includes lime, silica, iron oxide and manganese oxide. These particles are very fine and are usually carried by the air currents to the dust collector. When treated with water the insoluble particles are settled out to form a mud which is usually recovered by use of a filtering process. This mud includes fine particles of coke, iron oxide, oils and grease.
The fine materials above described are waste materials in that they cannot be effectively utilized in the usual commercial processes employed in the production and treatment of iron and steel. Further, the disposition of these waste materials is a problem to the industry because when allowed to accumulate, these materials come into great volume. However, they do contain from 30 to 80 weight percent of iron oxide and usually from 2 to 15 weight percent of combustible materials such as coke, oil or grease. Dust from steel making furnaces may have relatively small amounts of combustibles, such as from 0 to 3 percent, but flue dust from blast furnaces may have relatively large amounts of combustibles, such as from 10 to 60 percent. Such materials may be blended to form a mixture that has the desired amount of fuel. They may also contain small quantities of calcium oxide, magnesium oxide, and aluminum oxide. It would be very desirable if a way could be found to efficiently process these materials to make them acceptable as charging materials in a blast furnace. Accordingly, I have sought to find processes and apparatus which will accomplish this purpose, and I have discovered the improved process and apparatus which will now be set forth.